Add confidence interval for sign test
Merge pull request #12 from BigCrunsh/ci_for_sign_test

Add confidence interval for sign test
Add Kruskal-Wallis test
Emphasise approximation and clean-up

- change copyright
- use tiedrank_adj from wilcoxon.jl to be more consistent and efficient
- replace split helper function by explicitly looping to be more
  efficient
- add documentation to bring asymptotic approximation to attention and
  add warning for small group sizes.
Merge pull request #14 from BigCrunsh/add_kruskal_wallis

Add Kruskal-Wallis test
Clarify presentation of test functions

Clarify relationship between the observed value (to which null hypothesis
relates), the test statistic, and the confidence interval.

- added and printed out meta function "population_param_of_interest"
  to clarify between observation w/ confidence interval and actually
  test statistic.
- add show_params to describe meta data of a test (e.g., contingence
  table) and unify pretty print
- group point estimate and confidence interval to test summary
- unify t-test code
Separate Wilcoxon and Mann-Whitney test

These two tests use similar functionality but are actually different.

- add common file to extract helper functions
- clean up Wilcoxon and Mann-Whitney
- adapt function to pretty print
Add meta infos to circular tests
Merge pull request #13 from BigCrunsh/add_test_statistic

Clarify presentation of test functions and parameters
WIP Add confidence interval for Fisher exact test
WIP distinguish between central and minlike Fisher test

There are mulitple ways to define a p-value for the Fisher, or more
general, for 2 x 2 table test.  In order to implement
strongly consistent confidence intervals w.r.t the corresponding test,
we need to invert the corresponding test. Unfortunately, inverting the
minlike test does not necessarily lead to an interval. Thus, the default
version should be the central p-value with the corresponding interval.